Impact force measurements and energy calculations were performed on five embalmed cadaveric femora and an intact cadaver undergoing composite hip stem insertion using standard surgical methods. In addition, the number of impacts required to fully seat each stem was recorded.

The mean hammer velocity at the instant of impact was 5.15 ± 0.14 m/s and six impacts were required to fully seat the stem in all cases. The mean impact force was 6.20 ± 0.15 kN for the isolated femurs and 5.83 ± 0.67 kN for the cadaver. The mean impact energy was calculated to be 4.50 ± 0.54 J for the isolated femurs and 4.55 ± 0.43 J for the cadaver. Microscopic examination of the stems revealed no evidence of surface damage in any of the tests.

The forces and energies associated with intraoperative impact as measured in this study are sufficiently large to be of concern when considering the introduction of composite materials as replacements for metals in hip femoral components. Impact testing should be woven into the test scheme for both candidate composite materials and for different hip designs using these materials.